The icy planet LaMetal, the rarely-seen tenth planet orbiting on the borders of the solar system, has an elliptical course which causes it to cross paths with Earth every 1000 years. Unfortunately, this near-collision wreaks great havoc and destruction on Earth, and every millennium civilization must rebuild itself, only to be struck down the next time. LaMetal's world is inhabited by a subterranean humanoid kingdom that abducts a large number of humans during the devastation on Earth, and enslaves them. To ensure this, a woman from LaMetal is dispatched to live on Earth for 1000 years to collect the humans in preparation for LaMetal's arrival. This millennium, the princess of LaMetal has been living on Earth, under the name of Yukino Yayoi. However, an unexpected development occurs: Yayoi has come to care for her family and friends on Earth, and decides to fight to protect the Earth from LaMetal.